The present invention relates to motor driven bells operatively including a gong and motor driven hammer.
U.S. Pat. Nos. 4,692,741 and 4,368,458 disclose prior art motor driven bells incorporating a gong and motor driven hammer. FIGS. 1 and 2 show the prior art bell of U.S. Pat. No. 4,368,458. Such a bell comprises a cam member 20 connected to a driving shaft 22 of a motor 24. The cam member 20 acts on a leaf spring 26 for impelling a hammer 28 which is attached to the leaf spring 26, thereby causing the hammer to strike against a gong 30. With such a bell, however, the following problems exist:
1. Fluctuations in the electrical power delivered to the bell results in variation in both the frequency and amplitude of the displacement of the leaf spring.
2. Over time, the physical characteristics and hence the natural frequency of the leaf spring changes.
3. As a result of 1 and 2 above, a mismatch is likely to develop between the naural frequency of the leaf spring and the frequency at which its associated hammer are impelled by the cam member.
In such a case, the leaf spring and impelling cam member may operate antagonistically with each other resulting in diminished striking power of the hammer against the gong, and damping of the strength of the striking contact between the hammer and the gong.
4. In bells of the prior art design, the incorporated leaf spring is prone to mechanical deterioration which further aggravates the above described problems.